This invention relates to methods and compositions for producing stable disinfectants (such as chloramine) for use as a biocidal composition. Industrial water systems are subject to various sorts of fouling. Fouling can occur in the form of mineral fouling, biological fouling, and often combinations of the two. In fact mineral fouling often provides an anchor and substrate for biological infestations, and some organisms leach or secrete minerals onto industrial water system surfaces.
Fouling may occurs as a result of a variety of mechanisms including deposition of air-borne and water-borne and water-formed contaminants, water stagnation, process leaks, and other factors. If allowed to progress, fouling can cause a system to suffer from decreased operational efficiency, premature equipment failure, loss in productivity, loss in product quality, and (in particular in the case of microbial fouling) increased health-related risks.
Biological fouling results from rapidly spreading microbial communities that develop on any wetted or semi-wetted surface of the water system. Once these microorganisms are present in the bulk water they will form of biofilms on the system's solid surfaces.
Exopolymeric substance secreted from the microorganisms aid in the formation of biofilms as the microbial communities develop. These biofilms are complex ecosystems that establish a means for concentrating nutrients and offer protection for growth. Biofilms can accelerate scale, corrosion, and other fouling processes. Not only do biofilms contribute to reduction of system efficiencies, but they also provide an excellent environment for microbial proliferation that can include pathogenic bacteria. It is therefore important that biofilms and other fouling processes be reduced to the greatest extent possible to maximize process efficiency and minimize the health-related risks from water-borne pathogens.
Several factors contribute to the problem of biological fouling and govern its extent. Water temperature; water pH; organic and inorganic nutrients, growth conditions such as aerobic or anaerobic conditions, and in some cases the presence or absence of sunlight, etc., can play an important role. These factors also help in deciding what types of microorganisms might be present in the water system.
Many different Prior Art approaches have been attempted to control biological fouling of industrial processes. The most commonly used method is the application of biocidal compounds to the process waters. The biocides applied may be oxidizing or non-oxidizing in nature. Due to several different factors such as economics and environmental concerns, the oxidizing biocides are preferred. Oxidizing biocides such as chlorine gas, hypochlorous acid, bromine derived biocides, and other oxidizing biocides are widely used in the treatment of industrial water systems.
One factor in establishing the efficacy of oxidizing biocides is the presence of components within the water matrix that would constitute a chlorine demand or oxidizing biocide demand. Chlorine-consuming substances include, but are not limited to, microorganisms, organic molecules, ammonia and amino derivatives; sulfides, cyanides, oxidizable cations, pulp lignins, starch, sugars, oil, water treatment additives like scale and corrosion inhibitors, etc. Microbial growth in die water and in biofilms contributes to the chlorine demand of the water and to the chlorine demand of the system to be treated. Conventional oxidizing biocides were found to be ineffective in waters containing a high chlorine demand, including heavy slimes. Non-oxidizing biocides are usually recommended for such waters.
As described in U.S. patent application Ser. Nos. 12/546,086 and 11/618,227, Chloramines are effective and are typically used in conditions where a high demand for oxidizing biocides such as chlorine exists or under conditions that benefit from the persistence of an oxidizing biocide. Domestic water systems are increasingly being treated with chloramines. Chloramines are generally formed when free chlorine reacts with ammonia present or added to the waters. Many different methods for production of chloramines have been documented. Certain key parameters of the reaction between the chlorine and the nitrogen source determine the stability and efficacy of the produced biocidal compound.
Prior Art methods of producing chloramines have been described for example in U.S. Pat. Nos. 7,285,224, 6,132,628, 5,976386, 7,067,063, and 3,254,952 and US Published Patent Application and 2007/0123423. The Prior Art methods generally rely on the combination of an ammonium stabilizer component and a sodium hypochlorite component in a dilute or concentrated form to produce a solution of chloramines followed by immediate introduction into the water system being treated. Also typically the combination of the chemical components is conducted in a continuous and synchronous fashion in a conduit. To achieve this the components are either added to separate diluent (such as water) streams followed by the combination of the different streams containing the diluted components or the components are added simultaneously to the same stream at different locations, or the concentrated from of the components are combined. The components comprise a nitrogen source typically in the form of a ammonium salt (such as a sulfate, bromide, or chloride) and a chlorine or Bromine donor in the form of gas or combined with alkali earth metal (such as sodium, potassium, or calcium). Also the prior art methods have relied upon controlling the pH of the mixed solution by addition of a component at a high pH or by the separate addition of a caustic solution.
The limitations of these Prior Art methods have imposed a number of drawbacks on their use. Most limiting is the fact that the produced chloramine must be immediately used and cannot be stored for future use because it is subject to rapid degradation. The chloramine also must be generated outside of the system being treated and must be rapidly piped in to the system. As a result various economic, efficiency, and process, constraints limit the use and practicality of these Prior Art methods. Thus there is clear need and utility for a methods and compositions useful in improving the production and use of stable chloramine for use as a biocidal composition.
The art described in this section is not intended to constitute an admission that any patent, publication or other information referred to herein is “Prior Art” with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 CFR §1.56(a) exists.